Question

what causes the styrofoam to disappear into the acetone?

Explanation:

Styrofoam is a polystyrene - based material. Acetone is a solvent. Polystyrene is soluble in acetone. The acetone breaks down the polystyrene's long - chain structure, causing it to dissolve.

Answer:

Styrofoam (polystyrene) is soluble in acetone, and acetone breaks down its structure causing it to dissolve.